Some medical instruments can reduce the invasiveness and potential trauma previously associated with various medical procedures. The removal of stones such as kidney stones, gallstones, and the like from the body is one area where certain instruments are being used with some success. Various instruments can permit the removal of stones and other material from the body without the need for major surgery. Generally, a grasping device is guided through the body to the site of the stone and is used to grasp and remove the stone under the guidance of an endoscope.
Some of these instruments incorporate miniaturized grasping forceps. Others incorporate a retrieval basket as shown and described in U.S. Pat. No. 4,590,938 to Segura et al., U.S. Pat. No. 5,496,330 to Bates et al., and U.S. Pat. No. 5,658,296 to Bates et al. Known devices generally have a wire basket within a sheath, and the basket and the sheath move relative to each other to open and close the basket.
One problem with known baskets is that it often is difficult to remove the basket containing the material from the body without damaging the surrounding tissue and it is not possible to release the captured material from the basket. In some instances, a stone is of such a size that it is incapable of being removed while it is captured within the basket. In other instances, the body duct or orifice, such as the ureter or ureteral orifice junction (where the ureter and bladder join), is too small to allow for passage of the basket with the captured stone. If an excessive force is used to attempt to remove the basket and the captured material, tissue may be damaged. Sometimes surgery is required to dislodge both the basket and the captured material.